The present embodiments relate to medical ultrasound imaging catheters. A patient is scanned using an acoustic array of a catheter in the patient, providing real-time images from within the patient. The ultrasound imaging may assist with diagnosis or treatment. One such imaging catheter is a volume intra-cardiac echography (ICE) imaging catheter, the AcuNav V from Siemens. The array uses a helical twist of the face of the array to scan along different planes using different apertures.
To determine a position of the array in the patient, x-ray opaque markers in the catheter are detected with x-ray imaging (e.g., fluoroscopy). However, the relationship of the array to the markers must be known to relate the scan position of the array relative to the position of the catheter. To create the catheter, an acoustic array and markers are positioned in the catheter. Inexact positioning of the array in the catheter relative to the markers may cause misalignment problems.
The catheter is positioned in the patient through a guide or introducer. However, the catheter, and acoustic array in particular, may be damaged by insertion into a guide. For example, arrays with lengths of 7 mm or 14 mm may buckle, possibly damaging the array. Buckling of the array may adversely affect the safety and efficacy of the catheter. Longer arrays may allow for a scan of a larger volume, but may be more susceptible to buckling. Euler's formula for slender columns, where one end is fixed and the other end is free, is given as:
  P  =                    π        2            ⁢      IE              4      ⁢              L        2            where P=total ultimate load, I=least moment of inertia, E=elastic modulus, and L=column length. This formula may be used to estimate the relative resistance to buckling as a function of array length. Assuming a solid cylinder,
  I  =            π      ⁢                          ⁢              d        4              64  where d=column diameter. Combining these equations yields:
  P  =                              π          3                ⁢                  d          4                ⁢        E                    256        ⁢                                  ⁢                  L          2                      =                  kd        4                    L        2            After normalizing to a given length (e.g., 7 mm), a 28 mm long array may have approximately 15% of the buckling resistance as compared to the array of the given length, even with a change in diameter from 10 Fr to 12.5 Fr. Longer arrays are more likely to suffer costly damage due to buckling when inserted into the patient.